Default Group mms

Hey guys I was wondering if I can get some help on a group message app I've been using. I only 200mb of data and I can't leave my data running all day and most of my family use mms to group message each other. I've been using chomp sms which is a good app but if I have my data off I don't get any notifications when I get an mms until I turn on my data. What I want to do is to receive notifications with my data off then I can download the messages a contribute to the thread. Am I doing something wrong or is one of my settings off? Please help.

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